RU2465995C2 - Device and method for combined machining of shaped thin-wall part - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to combine machining of shaped part. Proposed method comprises the following stages. Cutter from conductive material with nonconductive abrasive material is revolved. Electric power is fed to machined part and cutter from power supply. Coolant is circulated there between. Note here that said coolant comprises one or more additives intended for increasing electric discharge between cutter and part. Part is arranged to preset cutting depth relative to cutter to be displaced relative to part for part roughing. In roughing, material is removed at relatively high intensity using high-speed electroerosion. Note here that power source provided first differential potential while coolant circulates at first flow rate and at first pressure. Cutter to be displaced relative to part for part finishing. In finishing, material is removed with relatively low intensity using precision electrolytic grinding. Note here that power source provided second differential potential while coolant circulates at second flow rate and at second pressure.

EFFECT: optimised cutting time and part clamping.

17 cl, 5 dwg

Description

State of the art

The invention relates generally to the processing of improved material, and in particular to the combined processing of a shaped workpiece with thin walls, such as a part with an aerodynamic profile of a gas turbine engine.

Thin-wall shaped metal parts are often difficult and expensive to process. Cost increases when parts are made of specialized alloys such as titanium alloys and the like. Such parts often cannot be accurately cast without the need for some finishing operations. Moreover, precision casting adds significant value even to relatively simple forms. In some circumstances, parts are made from oversized metal blanks and machined to their final shape using a technique known as flat milling. This process is intensive relative to the total processing time, tool cost and often requires specialized fastening accuracy when the part has thin walls or is non-rigid. Thus, there is a need to develop an alternative method that aims to optimize cutting time, processing time, fastening and tool cost.

Disclosure of invention

Briefly, an electrophysicochemical processing device for combined processing of a workpiece comprises a mandrel for supporting the workpiece; a cutter mounted on a spindle, wherein the cutter is made of an electrically conductive material and has a non-conductive abrasive material; an energy source for providing a differential electric potential between the workpiece and the cutter; a coolant source for circulating the coolant at a certain flow rate and pressure between the cutter and the workpiece; and means for moving the cutter relative to the workpiece, the material being removed from the workpiece with a relatively high material removal rate using a high-speed EDM process (HSEE), in which the energy source provides the first differential electrical potential and the coolant circulates at the first flow rate and under the first pressure, and the material is removed from the workpiece with a relatively low intensity of material removal using zovaniem process precision elektroshlifovaniya (PEG), wherein the power supply provides a second differential electrical potential and the coolant circulates at a second flow rate and at a second pressure.

According to another aspect of the invention, a method for combined processing of a workpiece is provided, comprising the steps of:

rotating a cutter made of an electrically conductive material and having a non-conductive abrasive material;

supplying electricity to the workpiece and cutter from an energy source;

provide circulation of the coolant between them, and the coolant contains one or more additives to increase the electric discharge between the cutter and the workpiece;

position the workpiece relative to the cutter at a given cutting depth;

the cutter is moved relative to the workpiece to remove material from the workpiece in the roughing operation, in which material is removed from the workpiece with a relatively high material removal rate using the high-speed electric discharge machining process (HSEE), while the energy source provides the first differential electric potential, and the coolant circulates at a first flow rate and at a first pressure; and

the cutter is moved relative to the workpiece to remove material from the workpiece in the finishing operation, in which the material is removed from the workpiece with a relatively low rate of material removal using the precision electric grinding (PEG) process, the energy source providing a second differential electric potential and the cooling medium circulates at a second flow rate and at a second pressure.

According to another aspect of the invention, a method for combined processing of a workpiece is provided, comprising the steps of:

rotating a cutter made of an electrically conductive material and having a non-conductive abrasive material;

supplying electricity to the turbine blade and the cutter from the energy source;

provide circulation of the coolant between the turbine blade and the cutter, the coolant containing one or more additives to increase the electric discharge between the turbine blade and the cutter;

positioning the turbine blade relative to the cutter at a first predetermined cutting depth;

the cutter is moved relative to the turbine blade in the roughing operation, in which the material is removed from the turbine blade with a relatively high material removal rate using the high-speed electric discharge machining process (HSEE), while the energy source provides the first differential electric potential and the coolant circulates at the first speed flow and under first pressure; and

the cutter is moved relative to the turbine blade in the finishing operation, in which the material is removed from the turbine blade with a relatively low material removal rate using the precision electro-grinding (PEG) process, the energy source providing a second differential electric potential and the coolant circulating at a second flow rate and under the second pressure.

Brief Description of the Drawings

These and other signs, features and advantages of the present invention will become clearer when reading the following detailed description with reference to the accompanying drawings, in which like elements are denoted by the same reference numerals in all the drawings and in which:

Figure 1 is a schematic illustration of an electrophysicochemical processing device for combined processing of a workpiece, such as a turbine blade, according to an embodiment of the invention;

Figure 2 is a perspective view of a turbine blade made using the combination machine shown in Figure 1, in accordance with the method according to the invention;

Figure 3 is a section of a turbine blade made along line 3-3 of Figure 2;

Figure 4 is a black and white micrograph of the inside of the turbine blade shown in Figure 2, after using the method according to the invention;

Figure 5 is a black and white micrograph of the granular structure of the inner part of the turbine blade shown in Figure 2.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the drawings, in which the same reference numbers denote the same elements in all different types, Fig. 1 shows an electrophysicochemical processing device, or a combination machine 10, which is capable of roughing and finishing machining a workpiece 50, especially a shaped one. workpiece with thin walls.

The combination machine 10 is configured to use both an improved high-speed electrical discharge machining (HSEE) process and an improved precision electric grinding (PEG) process, in which the combination machine 10 utilizes rapid thermal ablation, mechanical abrasion, and electromechanical dissolution processes. As a result of this, the combined machine 10 has the ability to perform various surface treatments and metal removal rates depending on the intensity (flow and pressure) of the electrolyte watering, the feed speed of the machine, the tool material and the differential electric potential between the anode and cathode.

During roughing, metal removal rates of approximately cubic inches per minute are possible with relatively high differential electric potentials and high pressure and electrolyte watering flows. In this first cutting mode, electrochemical discharges dominate during processing, which realize a high rate of metal removal. During finishing, metal removal rates are relatively low with relatively low differential electrical potentials and low pressure and electrolyte sprinkling fluxes. In this second cutting mode, electrochemical reactions and periodic light surface abrasion predominate during processing. Thus, the combined machine 10 is able to carry out two different cutting modes, which are especially useful when machining a thin-walled non-rigid structure more quickly than through conventional processes, while saving money on the tool by eliminating the need for precision casting of a thin-walled non-rigid structure.

In general, the combination machine 10 includes a support shaft or mandrel 12 on which the workpiece 50 is firmly mounted and supported with it. A circular cutting wheel or cutter 14 is fixedly mounted on a rotating shaft or spindle 16 for rotation with it during operation . The multi-axis carriage 18 is suitably configured to support the spindle 16 and the cutter 14 and provides drive means for moving the rotary cutter 14 relative to the workpiece 50 along the horizontal axis A during operation. Both the carriage motor 18 and the mandrel motor (not shown) are controllably connected to a digital programmable controller 20, which is specially configured with appropriate software to control all operations of the electrophysicochemical processing device or combination machine 10. In an exemplary embodiment of the invention the linear speed of the rotary cutter 14 is in the range between about 3 inches per minute and about 50 inches per minute, and more redpochtitelno between about 15 inches per minute and about 50 inches per minute. It should be understood that the invention is not limited by the linear speed of the rotating cutter, and that the removal rate of material from the workpiece can be maximized, while achieving the appropriate rough surface treatment of the workpiece.

CNC multi-axis machines or CNC machines are usually available and can be modified to introduce the desired linear movement of the rotary cutter 14 relative to the workpiece 50. For example, a combination machine 10 may comprise a 3-5-axis CNC machine such as a type that is well known in the art. Despite the fact that the workpiece 50 is held stationary when the rotating cutter 14 is correspondingly moved relative to it, the workpiece 50 can also move accordingly with respect to the cutter 14.

In an exemplary embodiment, the cutter 14 is made of an electrically conductive material, such as copper, with a non-conductive abrasive material such as alumina, ceramic, diamond, and the like uniformly distributed therein. Alternatively, the abrasive material may cover the outer surface of the conductive material. The grain size of the cutter 14 is in the range from about 60 grains to about 340 grains, and more preferably in the range from about 80 grains to about 200 grains, and most preferably is about 100 grains.

The corresponding energy source 22, both unchanging direct current and pulsed direct current, provides means for powering or supplying electric energy to the workpiece 50 and the cutter 14 during operation. The electric power source 22 includes a first negative (-) wire electrically conductively connected to the cutter 14 in any suitable manner, such as using a slip ring attached to an electrically conductive spindle. The second positive (+) wire electrically conductively connects the energy source 22 to the workpiece 50 in any suitable way, such as using another slip ring with an electrically conductive mandrel or directly attaching to the workpiece 50.

In the combined process of electrophysicochemical treatment, energy is supplied to the cutter 14, as to the cathode (-), and energy is supplied to the workpiece 50, as to the anode (+), to realize the differential electric potential between them. This differential electric potential between the cutter 14 and the workpiece 50 can be relatively higher for rapid electroerosion of the material from the workpiece 50. For example, during roughing, during the first cutting mode, the differential electric potential can be about 10 volts or more, and preferably about 14 volts. On the other hand, during finishing, during the second cutting mode, the differential electric potential can be relatively low, for example, below about 10 volts, to obtain a smooth surface of the workpiece 50, especially when smooth processing of thin walls of the workpiece 50 is carried out.

In order to maximize the removal of material by the rotary cutter 14, the cutter 14 can be made as wide as practical for cutting in one pass to minimize the need for additional passes or to remove material from the workpiece 50. Accordingly, the cutter 14 shown in figure 1, has the shape of a disk and the like.

During the combined process of electrophysicochemical electrical abrasion, considerable heat is generated, and the cutter 14 can rotate at the appropriate speed by means of a suitable motor (not shown) located in the carriage 18 to distribute the heat load around the perimeter of the cutter 14 during the operation. To minimize heat increase, the coolant source 24 includes an exhaust nozzle 28 that provides means for discharging a cutting fluid or liquid coolant 26 into the cutting zone between the cutter 14 and the workpiece 50 during an operation. In an exemplary embodiment of the invention, the coolant 26 is pumped through the nozzle 28 and sent to the gap between the rotating cutter 14 and the workpiece 50 with a given pressure and flow rate. Lubricating-cooling fluid or coolant 26 performs additional tasks of washing chips from the cutting zone, while cooling both the workpiece 50 and the cutter 14.

During the high metal removal rate of the first cutting mode, the flow and pressure of the coolant 26 are relatively high compared to what is available during the relatively low metal removal rate of the second cutting mode. For example, the pressure may be between about 100 psi and about 400 psi, and the flow rate may be between about 5 gal / min and about 50 gal / min during the first cutting mode. On the other hand, during a relatively low metal removal rate of the second cutting mode, the pressure may be less than about 200 psi and the flow rate may be between about 5 gal / min and about 50 gal / min. It should be understood that the pressure and flow of the coolant 26 during both the first and second cutting conditions depend on the direction in which the coolant 26 acts on the workpiece 50. As will be appreciated, the force exerted by the coolant 26 on the surface of the workpiece 50 is greater when the direction of the coolant is perpendicular to the surface of the workpiece 50, while the force exerted by the coolant 26 is less when the direction of the coolant State 26 is not perpendicular to the surface of the workpiece 50.

In an exemplary embodiment, the cutting fluid or coolant 26 contains one or more additives or other means to increase the conductivity of the coolant 26. For example, the coolant 26 may contain a halide salt such as sodium bromide, acid, base and things like that. In one embodiment, the coolant 26 contains sodium bromide in an amount of about 3-20% by weight to increase the plasma discharge (arc) between the workpiece 50 and the cutter 14. It is worth noting that the electrolyte conductivity is also important for the second cutting mode, in which electrochemical effect prevails? The conductivity of the solution is more important for the electrochemical reaction and probably does not necessarily contribute to plasma discharges. For example, coolant 26 may contain sodium bromide in an amount of about 5.4% by weight. Coolant 26 may also contain an additive to clean the pump, one or more rust preventative agents and the like. However, it should be understood that the invention is not limited to additives in the coolant, and that any suitable coolant that will improve plasma discharge can be used.

In some embodiments, the cutting zone of the workpiece 50 can be completely immersed in the coolant 26 to provide excellent heat dissipation and to facilitate the presence of coolant in the entire cutting zone. Dipping will hold back and cool the removed chips. When the cutting zone is completely submerged, the processing process can be used with or without additional direct watering of the cutting zone from the nozzle 28.

Combined machine 10 can be used to form a wide variety of shaped thin-walled parts. With reference to FIGS. 2 and 3, a combination machine 10 can be used, for example, to form a turbine blade, generally indicated at 100. To form a turbine blade 100, a workpiece 50, such as a turbine blade blank, is attached to the mandrel 12 of the combined device 10. The workpiece 50 is located relative to the cutter 14 so as to form the desired depth of cut. The workpiece 50 and the cutter 14 are powered by electricity from an energy source, and a coolant 26 circulates between them.

Then, the rotary cutter 14 is moved relatively for electrical erosion or machining of the workpiece 50 to perform a roughing operation using an improved high-speed EDM process (HSEE), in which the combination machine 10 uses thermal, mechanical abrasion and electrochemical dissolution processes to form the overall profile of the blade 100 turbines. The overall profile of the turbine blade 100 comprises outer surfaces 102a, 102b, inner surfaces 104a, 104b, an outer toe or a front metal edge 106a, an inner surface 106b that has a radius R for smoothly mating with the inner surfaces 104a, 104b, and conical ends 108, 110 The inner surfaces 104a, 104b are separated by a cavity 112 between them. In the shown embodiment, the turbine blade 100 has a thickness T1 of from about 0.002 inches to about 0.003 inches at ends 108, 110. However, conical ends 108, 110 may have a thickness of up to about 0.010 inches. The thickness T2 between the outer and inner surfaces 102a, 104a and 102b, 104b is from about 0.20 inches to about 0.50 inches.

As mentioned above, the roughing operation involves the first cutting mode of the combined machine 10, in which electrochemical discharges, which realize a high metal removal rate, predominate during processing. In this first cutting mode, the differential electric potential between the cutter 14 and the workpiece 50 is 10 volts or higher. In addition, the pressure of the coolant 26 is in the range between about 100 psi and about 400 psi, and the flow rate can be in the range of about 5 gal / min to about 50 gal / min. The gap between the cutter 14 and the surface of the workpiece 50 depends on the required plasma discharge field (arc) and the grain size of the abrasive non-conductive material of the cutter 14. For example, the diameter of the abrasive particles equal to 100 grains is approximately 0.005 inches. In an exemplary embodiment, the clearance is in the range of about 0.005 to 0.009 inches.

After the overall profile of the turbine blade 100 has been formed using the first cutting mode, the rotary cutter 14 is then moved relatively for electrical erosion or machining of the workpiece 50 to carry out the finishing operation using the improved precision electric grinding (PEG) process in which the combination machine 10 uses both abrasion and electromechanical dissolution processes.

As mentioned above, the finishing operation involves a second cutting mode of the combined machine 10, in which electrochemical reactions and periodic slight abrasion of the surface predominate during the processing. In this second cutting mode, the differential electric potential between the cutter 14 and the workpiece 50 is less than 10 volts. In addition, the pressure of the coolant 26 is less than about 200 psi, and the flow rate can range from about 5 gal / min to about 50 gal / min.

In the finishing operation, the overall profile of the turbine blade 100 is machined to form the finished surfaces of the finished turbine blade 100. The use of the finishing operation of the second cutting scheme eliminates and / or reduces the need for precision casting, which is a very expensive component in the manufacture of parts formed mainly from thin-walled structures.

A series of tests was performed on a part made of titanium to study the effects of various operating parameters on the results obtained by using the first and second cutting modes of the combined machine 10. The operating parameters that were investigated included linear speed (inches per minute), current (amperes), the concentration of sodium bromide (NaBr) in the coolant (as a percentage of weight) and the size of the zone exposed to heat (HAZ) (thousands of inches). The research results are shown in table 1 below.

Table 1 The impact of various parameters on the first and second cutting modes Detail Linear speed Current NaBr Haz ipm A % mil 17 25 270 3.6 10 eighteen thirty 290 3.6 fifteen 19 10 200 3.6 <5 23 thirty 290 5,4 fifteen 24 twenty 260 5,4 10 25 10 200 5,4 10

As shown in table 1, the use of both the high speed EDM process (HSEE) for roughing and the improved precision electric grinding (PEG) process for finishing gave good results for a wide variety of working conditions. In particular, the heat-affected area (HAZ) was an acceptable 0.015 inches or less in all test specimens. In part 19, the zone exposed to heat was less than 0.005 inches, with a linear speed of 10 ipm (inches per minute), the applied potential was 14 V, (the current is not an experimentally controlled variable and may not need to be mentioned) the current was 200 A and the NaBr concentration was 3.6 percent by weight. The heat-affected zone was the largest at 0.015 inches, when the linear velocity was the fastest at 30 ipm, even at different NaBr concentrations.

FIGS. 4 and 5 show microphotographs of part 25 close to the radius-curved inner surface 106. As shown in FIGS. 4 and 5, the use of both the high-speed electric discharge machining process (HSEE) for roughing and the improved precision electric grinding (PEG) process for finishing gives good results.

As a result, the first cutting mode, which uses the high-speed electric discharge machining process (HSEE) through the application of thermal, electric discharge and electrochemical processing at relatively high differential electric potential and the intensity of electrolyte irrigation, provides a combined synergistic improvement in the rates of metal removal compared to conventional processes, which only abrasion is used to remove the oxide layer to promote elemental intensities ctrochemical reactions. In addition, the second cutting mode, which uses the Precision Electro-Grinding (PEG) process through the use of moderate electroerosion processing, periodic abrasion and electrochemical processing with relatively low differential electric potential and electrolyte watering intensity, eliminates the need for precision casting, which is a very expensive component in the manufacture of parts formed mainly from thin-walled structures.

Although the embodiments shown have been described with reference to a turbine blade containing a titanium alloy, the invention is not limited to machining a turbine blade and can be used to a large extent for machining a variety of workpieces made from any metal material that is easy to process by grinding milling, turning and the like. Some non-limiting examples in which the process of the invention can be used include processing plates for use in armor, turning for manufacturing shafts, processing components for heat exchangers, and the like.

Examples are used in the description, including the preferred embodiment, to disclose the invention and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined in the claims and may include other examples that are encountered by those skilled in the art. Such other examples are intended to be included within the scope of the claims if they have structural elements that do not differ from the elements indicated in the claims, or if they include equivalent structural elements with insignificant differences from the elements indicated in the claims.

Claims (17)

1. A device for the combined processing of the workpiece, containing a mandrel to support the workpiece, the cutter mounted on the spindle, and the cutter is made of electrically conductive material and has a non-conductive abrasive material, an energy source to provide differential electrical potential between the workpiece and the cutter, a source of cooling substance for circulating a coolant with a certain flow rate and pressure between the cutter and the workpiece, and means d I move the cutter relative to the workpiece, which is configured to remove material from the workpiece with a relatively high rate of material removal using the high-speed EDM process (HSEE), in which the energy source provides the first differential electric potential and the coolant circulates at the first flow rate and under the first pressure, and the ability to remove material from the workpiece with a relatively low removal rate of ma material using a precision electric grinding (PEG) process in which the energy source provides a second differential electric potential and the coolant circulates at a second flow rate and at a second pressure. 2. The device according to claim 1, in which the first differential electric potential is equal to or greater than about 10 V, and the second differential electric potential is less than about 10 V. 3. The device according to claim 1, in which the first pressure is in the range between about 100 psi and about 400 psi, and wherein the second pressure is less than about 200 psi. 4. The device according to claim 1, in which the first and second flow rates are in the range between about 5 gal / min and about 50 gal / min. 5. The device according to claim 1, in which the workpiece is a turbine blade. 6. The device according to claim 1, in which the granularity of the non-conductive abrasive material is from about 60 grains to about 340 grains. 7. The device according to claim 1, in which the means for increasing the electric discharge contains one or more additives in the coolant. 8. The device according to claim 7, in which one or more additives contains sodium bromide. 9. A method of combined processing of a workpiece, comprising the steps of rotating a cutter made of an electrically conductive material and having a non-conductive abrasive material, supplying electricity to the workpiece and the cutter from an energy source, circulating the coolant between them, the coolant containing one or more additives to increase the electric discharge between the cutter and the workpiece, position the workpiece relative to the cutter at a given depth e cutting, move the cutter relative to the workpiece to remove material from the workpiece in the roughing operation, in which the material is removed from the workpiece with a relatively high rate of material removal using the high-speed electric discharge machining (HSEE), while the energy source provides the first differential electrical potential, and the coolant circulates at the first flow rate and at the first pressure, and the cutter is moved relative to the processing part to remove material from the workpiece in the finishing operation, in which the material is removed from the workpiece with a relatively low rate of material removal using the precision electro-grinding (PEG) process, wherein the energy source provides a second differential electric potential and the coolant circulates from the second speed, flow and second pressure. 10. The method according to claim 9, in which the first differential electric potential is equal to or greater than about 10 V, and the second differential electric potential is less than about 10 V. 11. The method according to claim 9, in which the first pressure is in the range between about 100 psi and about 400 psi, and the second pressure is less than about 200 psi. 12. The method according to claim 9, in which the first and second flow rates are in the range between about 5 gal / min and about 50 gal / min. 13. The method according to claim 9, in which the workpiece is a turbine blade. 14. The method according to claim 9, in which the granularity of the non-conductive abrasive material is from about 60 grains to about 340 grains. 15. The method according to claim 9, in which the means for increasing the electric discharge contains one or more additives in the coolant. 16. The method according to clause 15, in which one or more additives contains sodium bromide. 17. A method for the combined processing of a workpiece, comprising the steps of rotating a cutter made of an electrically conductive material and having a non-conductive abrasive material, supplying electricity to the turbine blade and the cutter from an energy source, circulating coolant between the turbine blade and the cutter, the coolant being contains one or more additives to increase the electric discharge between the turbine blade and the cutter, the turbine blade is positioned relative to the cutter on the first set at a lower depth of cut, the cutter is moved relative to the turbine blade in the roughing operation, in which the material is removed from the turbine blade with a relatively high material removal rate using the high-speed electric discharge machining process (HSEE), while the energy source provides the first differential electric potential and the coolant circulates at the first flow rate and at the first pressure, and the cutter is moved relative to the turbine blade in the finishing operation, at which This material is removed from a turbine blade with a relatively low material removal rate using a precision electric grinding (PEG) process, the energy source providing a second differential electric potential and the coolant circulating at a second flow rate and at a second pressure.

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